Carotid artery stenoses typically manifest in the common carotid artery, internal carotid artery or external carotid artery as a pathologic narrowing of the vascular wall, for example, caused by the deposition of plaque, that inhibits normal blood flow. Endarterectomy, an open surgical procedure, traditionally has been used to treat such stenosis of the carotid artery.
A important problem encountered in carotid artery surgery is that emboli may be formed during the course of the procedure, and these emboli can rapidly pass into the cerebral vasculature and cause ischemic stroke. Consequently, surgical procedures such as endarterectomy typically have high mortality rates.
In view of the trauma and long recuperation times generally associated with open surgical procedures, considerable interest has arisen in the endovascular treatment of carotid artery stenosis. In particular, widespread interest has arisen in transforming interventional techniques developed for treating coronary artery disease, such as angioplasty and stenting, for use in the carotid arteries. Such endovascular treatments, however, are especially prone to the formation of emboli.
Such emboli may be formed, for example, when an interventional instrument, such as a guide wire or angioplasty balloon, is forcefully passed into or through the stenosis, as well as after dilatation and deflation of the angioplasty balloon or stent deployment. Because such instruments are advanced into the carotid artery from a direction "upstream" of the direction of blood flow, emboli generated by operation of the instruments are carried "downstream" by normal antegrade blood flow--directly into the brain.
Several previously known apparatus and methods attempt to removing emboli formed during endovascular procedures by trapping or suctioning the emboli out of the vessel of interest. These previously known systems, however, provide less than optimal solutions to the problems of effectively removing emboli.
Solano et al. U.S. Pat. No. 4,921,478 describes cerebral angioplasty methods and devices wherein two concentric shafts are coupled at a distal end to a distally-facing funnel-shaped balloon. A lumen of the innermost shaft communicates with an opening in the funnel-shaped balloon at the distal end, and is open to atmospheric pressure at the proximal end. In use, the funnel-shaped balloon is deployed proximally (in the direction of flow) of a stenosis, occluding antegrade flow. An angioplasty balloon catheter is passed through the innermost lumen and into the stenosis, and then inflated to dilate the stenosis. The patent states that when the angioplasty balloon is deflated, a pressure differential between atmospheric pressure and the blood distal to the angioplasty balloon causes a reversal of flow in the vessel that flushes any emboli created by the angioplasty balloon through the lumen of the innermost catheter.
While a seemingly elegant solution to the problem of emboli removal, several drawbacks of the device and methods described in the Solano et al. patent seem to have lead to abandonment of that solution. Chief among these problems is the inability of that system to generate flow reversal during insertion of the guide wire and the angioplasty balloon across the stenosis. Because flow reversal does not occur until after deflation of the angioplasty balloon, there is a substantial risk that any emboli created during placement of the angioplasty balloon will have traveled too far downstream to be captured by the flow reversal. It is expected that this problem is further compounded because only a relatively small volume of blood is removed by the pressure differential induced after deflation of the angioplasty balloon. These same drawbacks appear to have prevented commercialization of a similar system described in EP Publication No. 0 427 429.
Kletschka U.S. Pat. No. 4,794,928 describes an angioplasty device and methods for removing emboli generated during angioplasty, comprising a catheter bundle having an expandable funnel-shaped trap/barrier disposed on its distal end. A removal lumen is situated within the trap/barrier so that a pressure differential generated between the proximal and distal ends causes the emboli to be removed from the trap/barrier. While the patent states that the funnel-shaped trap/barrier may be placed either proximal or distal to the stenosis, the patent illustrates the trap/barrier as being disposed in the direction of antegrade flow, and does not suggest causing flow reversal within a vessel.
Imran U.S. Pat. No. 5,833,650 describes a system for treating stenoses that comprises three concentric shafts. The outermost shaft includes a proximal balloon at its distal end that is deployed proximal of a stenosis to occlude antegrade blood flow. A suction pump then draws suction through a lumen in the outermost shaft to cause a reversal of flow in the vessel while the innermost shaft is passed across the stenosis. Once located distal to the stenosis, a distal balloon on the innermost shaft is deployed to occlude flow distal to the stenosis. Autologous blood taken from a femoral artery using an extracorporeal blood pump is infused through a central lumen of the innermost catheter to provide continued antegrade blood flow distal to the distal balloon. The third concentric shaft, which includes an angioplasty balloon, is then advanced through the annulus between the innermost and outermost catheters to dilate the stenosis.
Like the device of the Solano patent, the device of the Imran patent appears to suffer the drawback of potentially dislodging emboli that is carried into the cerebral vasculature. In particular, once the distal balloon of Imran's innermost shaft is deployed, flow reversal in the vasculature distal to the distal balloon ceases, and the blood perfused through the central lumen of the innermost shaft establishes antegrade flow. Importantly, if emboli are generated during deployment of the distal balloon, those emboli will be carried by the perfused blood directly into the cerebral vasculature, and again pose a risk of ischemic stroke. Moreover, there is some evidence that reperfusion of blood under pressure through a small diameter catheter may contribute to hemolysis and possible dislodgment of emboli.
In view of these drawbacks of the previously known emboli removal systems, it would be desirable to provide methods and apparatus that establish retrograde flow in a vessel at key stages throughout a surgical or interventional procedure, thereby reducing the risk that emboli are carried downstream.
It also would be desirable to provide emboli removal methods and apparatus that ensure that an adequate volume of blood is removed from the system to enhance the likelihood that emboli generated by a surgical or interventional procedure are effectively removed from the vessel of interest.
It still further would be desirable to provide emboli removal methods and apparatus that intermittently provide regional reversal of flow in a vessel, and thus avoid deployment of balloons or other devices distal to the stenosis to delimit a confined treatment field.